Microstructure and properties of fly ash-based geopolymeric material with 5A zeolite as a filler

Fly ash-based geopolymeric material with 5A zeolite as a filler was synthesized and the microsturture, compressive strength, formaldehyde adsorption property and efflorescence extent of the material obtained were investigated. The results showed that addition of 5A zeolite served to increase the compressive strength, which resulted from the micro-aggregate effect of fine zeolite particles on one hand and the enhancement of geopolymerization extent on the other hand. The Ca2+ diffused from 5A zeolite through ion exchange with Na+ in activator solution was assumed to be incorporated into the aluminosilicate framework as a charge-balancing cation to form a new fiber-like phase in the zeolite-contained geopolymer specimens. The fiber-like phase was suggested to be the amorphous zeolite-like hydrate products and the formation of this phase improved the geopolymerization through the mechanism of providing nucleation sites for geopolymer formation. In addition, the higher alkalinity of activator solution caused by the water adsorption of zeolite may also be responsible for the higher geopolymerization extent. The efflorescence extent of geopolymer specimen decreased with 5A zeolite addition, which is by reason of the Na+ fixation into the zeolite structure through Ca2+/Na+ exchange and the lesser pore volume of macropores. Moreover, 5A zeolite in geopolymer still exhibited excellent formaldehyde adsorption ability. Therefore, fly ash-based geopolymer with 5A zeolite addition is potentially applicable to the development of new construction materials with the ability of purifying indoor air pollutants.

► 5A zeolite is used to improve the properties of geopolymers.
► 5A zeolite addition in geopolymer improves the compressive strength and decreases the efflorescence extent.
► A new fiber-shaped phase similar to zeolite appears in geopolymers with 5A addition.
► Geopolymers with 5A zeolite addition exhibits excellent formaldehyde adsorption ability.